The invention relates to a flat link chain bucket conveyor which is constructed in particular as high-speed conveyor with centrifugal discharging, comprising a flat link chain and buckets secured to the flat link chain. The invention relates in particular to a novel securing of the buckets to the flat link chains.
It is known in the art to provide chain link plates with flanged or forged-on angle members for screwing on the buckets, cf. the "Special publication from Zement, Kalk, Gips", volume 26, 1974, no. 4, pages 176 to 181: "Vertical bucket elevators for hot material", published in the Bauverlag, Wiesbaden. According to a further embodiment it is known with a forged link plate form to provide bores at reinforced points via which the buckets are directly screwed to the link plate. In all known cases the bucket is fixedly screwed to the flat link chain. Usually, the screwing is even carried out with bracing means because the buckets themselves are rough welded members without machined securing faces. Due to the rigid connection all the shocks and vibrations transmitted to the chain are consequently further transmitted to the buckets or cups as well. As a result, a tearing of the bucket rear walls occurs very rapidly, this starting from the bores of the securing screws. Furthermore, the rear or front upper corners of the buckets are also very much endangered.
The cause of these impacts resides in particular in the polygon effect of the chain drive wheels which produces longitudinal oscillations in the chain (see "Special publication from Zement, Kalk, Gips", 27th volume, November 74, published in Bauverlag, Wiesbaden "Shuttle bucket elevators--the universal conveying means for the cement and lime industry"). These vibrations are also transmitted to the buckets.
When the chain runs onto the drive wheel the chain is also given a lateral jolt, this taking place at the instant at which the flat link chain bushing contacts the drive wheel and then has to follow the circular arc. The mass of the bucket and its contents engages at the center of gravity lying outside the chain and tends to press the lower bushing of the chain link plates inwardly, i.e. in the direction of the chain wheel, whilst the upper bushing is drawn outwardly, i.e. away from the chain wheel. As confirmed in practice the strike marks at the bushings lying below with respect to the bucket are greater than at the bushings lying above with respect to the bucket.
By the striking of the bushing on the chain wheel the chain and buckets are set in vibration. If this vibration is by chance with the inherent frequency of the buckets or close to this frequency destruction of the buckets within a short time is to be expected. It should also be pointed out in this connection that the bracing on securing of the buckets on the chain effects a change of the frequency behaviour. Mostly, there is a frequency displacement to dangerous higher frequencies. The occurrence of sheet metal and weld seam cracks can always be observed in time and in some cases the first cracks appear after only two months; they appear at the latest usually however after one year depending on the bucket design and sheet metal thickness.
When the upper chain bushing has come to bear on the chain wheel, a bending of the chain at the joint must be initiated. Measurements have shown that firstly the static friction must first be overcome by applying a considerably force and this again also leads to vibrations in the chain. By corresponding measurements the bending stress of the chain link plate in the highly loaded eye can be quite clearly detected by increasing of the tension force in the outer link plate portion and reduction thereof in the inner link plate portion.
To avoid sheet metal and weld seam cracks a great number of variations have already been considered of the bucket form, sheet metal thicknesses, material qualities, weld seam thicknesses, beads and reinforcements of the bucket rear walls and tested in fatigue tests. However, all the variations of shape and material fail to provide any appreciable success.